1. Field of the Invention
This invention generally relates to telephones and more specifically to a device for detecting the first dialed digit and for comparing it with a reference value to determine the type of a telephone call.
2. Description of the Prior Art
Commercially well known telephone has a capability to establish a telephone call of a selective type in accordance with the first dialed digit.
A telephone display accessory disclosed in U.S. Pat. No. 4,160,879 issued on July 10, 1979 to Ronald L. Sullivan et al. utilizes a binary counter to count pulses produced by a rotary dial in order to distinguish, by the absence or presence of a 1 as the first digit dialed, local calls, long distance calls within the calling area, and long distance calls outside the calling area.
The technique of counting dialed pulses is not usable in a DTMF (Dual Tone Multi-Frequency) dialing system.